基于前药原理设计、整合素受体介导的脑肿瘤靶向聚合物胶束递药系统研究

The blood brain barrier (BBB), tumor permeability and cell internalization are the main obstacle for the treatment of brain tumor. It was found that integrin receptor αvβ3 are highly expressed on both brain microvascular endothelial cells and glioma cells. As the substrate of αvβ3, tetraiodothyroacetic acid (Tetrac) is an efficient tumor targeting ligand. In the previous studies, we designed and synthesized a wheat-like derivative of D-α-tocopherol polyethylene glycol 1000 succinate (TPGS), PAMV6, which not only has good stability, long circulation time, but also can improve the brain uptake of chemotherapeutics. However, the targeting efficiency of PAMV6 micelles to brain tumor cells was not high. The active targeting strategy based on tetrac can make up for the defects. Thus, in our present project, we design a polymeric micelle system for BBB and brain tumor cell dual-targeting, by conjugation tetrac on the surface of PAMV6 via tumor microenvironment sensitive spacer. Afterwards, teniposide would be used as the model drug. The process of this micelle cross the BBB, permeation over tumor vasculature and internalization into tumor cells was studied on orthotopic glioma animal models. Moreover, the mechanism how the delivery system induced brain tumor endothelial cell apoptosis and inhibited the brain tumor malignant proliferation would be confirmed both in vitro and in vivo. Therefore, this project has never been reported, and will provide an alternative choice for the treatment of brain tumors.

血脑屏障、药物的肿瘤渗透和高效入胞是脑肿瘤靶向治疗需要克服的主要障碍。研究发现脑微血管内皮细胞和胶质瘤细胞均高表达整合素受体αvβ3，而四碘甲腺乙酸（Tetrac）作为αvβ3的底物，是一种高效的肿瘤靶向分子。本课题组前期设计合成的麦穗样结构的TPGS衍生物PAMV6胶束，稳定性好、体内循环时间长且能通过被动靶向增加化疗药物的脑部摄取，但其脑肿瘤靶向效率不足。以Tetrac为靶向头基的主动靶向策略可弥补这一缺陷。因此本项目拟将Tetrac通过肿瘤微环境敏感的二肽间隔基连接于PAMV6表面，设计一个能同时跨越BBB和富集于脑肿瘤细胞的双靶向聚合物胶束递药系统。本课题计划以替尼泊苷为模型药物，建立原位脑胶质瘤动物模型，研究该靶向给药系统经BBB摄取、跨过肿瘤血管屏障进而内吞进入脑肿瘤细胞的过程，阐明其诱导脑肿瘤血管内皮细胞凋亡、抑制脑肿瘤恶性增殖的作用机制，为脑肿瘤的靶向治疗提供新思路和方法。

血-脑屏障和血-脑肿瘤屏障的存在使得脑肿瘤的治疗仍是世界性难题。构建既能跨越血脑屏障又能高效渗透血-脑肿瘤屏障、进而进入脑肿瘤细胞的靶向递药系统是脑肿瘤治疗的关键所在。本项目根据脑微血管内皮细胞和脑胶质瘤细胞均高表达整合素受体αvβ3这一结构特点，以其小分子底物四碘甲腺乙酸（Tetrac）为双重靶向导向分子，以粒径适宜、稳定性好、且具有P-gp抑制活性的聚合物胶束材料PAMV6为载体，构建了一个能够同时跨过血脑屏障并富集于脑肿瘤细胞的双重级联靶向递药系统。构建的多功能聚合物胶束（Tetrac-PAMV6/THP）粒径为76.5 nm，呈类球形。Tetrac修饰的多功能聚合物胶束能够同时增强脑微血管内皮细胞bEnd.3及脑胶质瘤细胞C6对PAMV6胶束的摄取。细胞增殖、细胞周期及细胞凋亡等结果均显示Tetrac-PAMV6/THP胶束能够显著增强游离药物对脑肿瘤细胞的杀伤能力。活体成像结果显示，Tetrac修饰的多功能聚合物胶束Tetrac-PAMV6高效富集于脑肿瘤区域，具有很好的体内脑肿瘤靶向性。同时，Tetrac-PAMV6/THP胶束能够显著抑制脑肿瘤细胞的生长，延长荷胶质瘤小鼠的生存期。以上结果表明该项目成功构建了一种新型的脑肿瘤靶向递药系统，有望提高对脑肿瘤的治疗效果，为脑肿瘤的诊断和治疗提供了新思路，具有重要的研究意义和潜在的应用价值。